1. Field of the Invention
The present invention relates to an improved aperture device which is designed to disperse reflection of light to suppress degradation of image quality from an edge of an aperture component and also to an optical apparatus which incorporates the aperture device.
2. Description of the Related Art
It has been known that uncontrolled reflection of light inside a lens barrel causes a halo or ghost effect on the image plane which degrades the quality of the image. To avoid this problem, it has been proposed to apply a light-absorbing black paint to the inner surface of the lens barrel and the aperture blade surfaces to control reflection of light and thereby prevent degradation of the image quality.
However, taking of an image of a bright object such as the sun, tends to cause a radial ghost image formed around the object image. An analysis conducted by the present inventors has proved that such a ghost image is attributable to light reflected from the inner edge of the aperture's blades. The inner edge is that edge of the shutter blade which forms a side of the aperture.
FIG. 6 shows the state in which strong light impinges upon the inner edge of each aperture blade 10 of an iris aperture device. This strong light is reflected by the inner edge so as to cause a ghost image. FIG. 7 illustrates an aperture 11 defined by the inner edges of six blades, two of which are depicted by reference numerals 10, 10'.
The ghost image is generated in the direction perpendicular to the inner edge of each aperture blade defining the aperture, i.e., the edge of the aperture blade defining one side of a substantially polygonal aperture. Thus, the ghost image appears radially in six directions when six aperture blades are involved and in eight directions when eight aperture blades are used in the aperture device. Generation of a ghost image is more serious when the aperture diameter is small because in such a case the quantity of light reflected by the aperture blade edges constitutes a large proportion relative to the quantity of the imaging light.